Communication apparatus and method for controlling transmission power and communication apparatus

ABSTRACT

A communication apparatus ( 100 ), when synchronization of a received signal is established, performs transmit power control using a transmit power value obtained by closed-loop transmit power control by a transmit power control circuit ( 201 ), and when the synchronization of the received signal is out, controls a current transmit power value to gradually return over a predetermined period to a transmit power value determined at a timing closest to the current timing from among past reliable transmit power values determined when the synchronization was established.

TECHNICAL FIELD

[0001] The present invention relates to a communication apparatus usedin a mobile communications system using a CDMA (Code Division MultipleAccess) scheme and a transmit power control method for the communicationapparatus.

BACKGROUND ART

[0002] Conventionally, a mobile communications system using the CDMAscheme, the levels of signals received by a base station from mobilestations vary greatly depending on where the mobile station is located,and thus the far-near problem occurs that a received signal having largepower interferes with a received signal having small power. Inparticular, in a communication system using the CDMA scheme, a pluralityof mobile stations share the same frequency band, and hence for eachmobile station, signals from other mobile stations become interferencesignals and degrade the communication quality of its channel. Suchinterference associated with the far-near problem leads to the reductionof the number of multiple stations in the same cell.

[0003] One method for solving this problem is a transmit power controlcircuit disclosed in Laid-Open Japanese Patent PublicationNo.2001-69073. In this transmit power control circuit, information datasubjected to transmit power control and transmit power controlinformation not subjected to transmit power control are transmitted atthe same time from a base station to a mobile station, and the mobilestation determines the transmit power of a signal to be sent in returnto the base station based on the transmit power control information fromthe base station.

[0004] The transmit power is determined by estimating the receive levelof the signal from the base station, and, based on a result of reductionin this receive level, selecting a transmit power for a signal to besent in return to the base station.

[0005] When the receive level decreases at a mobile station, the mobilestation selects the transmit power of the signal sent at the previoustime in return to the base station under transmit power control as atransmit power for a signal to be sent in return to the base station.

[0006] A typical transmit power control apparatus thus controls thetransmit power using only the receive level of the received signal atthe mobile station, so that it is effective to a certain degree incontrolling the transmit power against instantaneous reduction in thelevel of the received signal due to fading and the like and interferencebecause of. However, changing the transmit power more than needed inresponse to instantaneous reduction in the level of the received signaland interference causes the transmit power value to vary suddenly andgreatly, and consequently the problem occurs that the closed-looptransmit power control is affected in a harmful way.

DISCLOSURE OF INVENTION

[0007] The object of the present invention is to provide a communicationapparatus and transmit power control method for the communicationapparatus that continues communication as long as possible withoutfollowing rapid changes in the received signal level and which,immediately after detecting that the communication is out, controlstransmit power.

[0008] According to an embodiment of the present invention, acommunication apparatus comprises a first transmit power control sectionthat receives a transmit signal transmitted from a mobile station orbase station and controls a transmit power value of a signal to transmitto the mobile station or base station based on the received signal; atransmit power value storage section that stores a predetermined numberof past transmit power values from the first transmit power controlsection; a synchronization determining section that detects asynchronous state of the received signal; and a second transmit powercontrol section that, upon detecting that the synchronous state is notmaintained based on a determination result of the synchronizationdetermining section, controls a transmit power value based on a pasttransmit power value, corresponding to a time the synchronous state wasmaintained, from among the past transmit power values stored in thetransmit power value storage section.

[0009] According to another embodiment of the present invention, atransmit power control method for the communication apparatus comprises:a first transmit power control step of receiving a transmit signaltransmitted from a mobile station or base station and controlling atransmit power value of a signal to transmit to the mobile station orbase station based on the received signal; a transmit power valuestoring step of storing a predetermined number of past transmit powervalues from said transmit power control step; a synchronizationdetermining step of detecting a synchronous state of the receivedsignal; and a second transmit power control step of controlling atransmit power value based on a past transmit power value, correspondingto a time the synchronous state was maintained, from among the pasttransmit power values stored in the storing step, upon detecting thatthe synchronous state is not maintained based on a result of thedetecting step.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram showing the configuration of acommunication apparatus according to embodiment 1 of the presentinvention;

[0011]FIG. 2 is a block diagram showing the configuration of asynchronization determining circuit of the communication apparatusaccording to embodiment 1 of the present invention;

[0012]FIG. 3 is a block diagram showing the configuration of a transmitpower determining circuit of the communication apparatus according toembodiment 1 of the present invention;

[0013]FIG. 4 is a flow chart for explaining the operation of thecommunication apparatus according to embodiment 1 of the presentinvention;

[0014]FIG. 5 is a schematic view for explaining the operation of thecommunication apparatus according to embodiment 1 of the presentinvention;

[0015]FIG. 6 is a block diagram showing the configuration of acommunication apparatus according to embodiment 2 of the presentinvention;

[0016]FIG. 7 is a block diagram showing the configuration a transmitpower determining circuit of the communication apparatus according toembodiment 2 of the present invention;

[0017]FIG. 8 is a flow chart for explaining the operation of thecommunication apparatus according to embodiment 2 of the presentinvention;

[0018]FIG. 9 is a block diagram showing the configuration of acommunication apparatus according to embodiment 3 of the presentinvention;

[0019]FIG. 10 is a block diagram showing the configuration a transmitpower determining circuit of the communication apparatus according toembodiment 3 of the present invention; and

[0020]FIG. 11 is a flow chart for explaining the operation of thecommunication apparatus according to embodiment 3 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] Embodiments of the present invention will be described in detailbelow with reference to the drawings. Note that the present invention isnot at all limited to these embodiments and can be implemented asvarious embodiments without departing from the spirit and scope of theinvention.

[0022] The framework concept of the present invention is that, when itis detected that the synchronous state of the received signal is notmaintained, the transmit power value is controlled based on a pasttransmit power value corresponding to a time the synchronous state wasmaintained, from among past transmit power values stored in a transmitpower storage section.

EMBODIMENT 1

[0023]FIG. 1 is a block diagram showing the configuration of acommunication apparatus 100 according to embodiment 1 of the presentinvention. As shown in FIG. 1, a communication apparatus 100 as a mobilestation apparatus comprises a transmit section containing a transmitdata conversion circuit 102, a modulation circuit 103, a spreadingcircuit 104, a transmit circuit 105, and a transmit antenna 106; and areceive section containing a receive antenna 107, a receive circuit 108,a despreading circuit 109, a demodulation circuit 110, and a receivedata conversion circuit 111.

[0024] The communication apparatus 100 further comprises, as a transmitpower control apparatus, a synchronization determining circuit 112 thatdetermines the synchronization of the received data obtained from thereceive section and a transmit power determining circuit 113 thatcontrols the transmit power based on the determining results of thesynchronization determining circuit 112.

[0025] The transmit data conversion circuit 102 forms an input signalinto a frame, generates transmit data by performing CRC-encoding andforward error correction(FEC) encoding on the frame signal, and suppliesthe transmit data to the modulation circuit 103.

[0026] The modulation circuit 103 modulates the transmit data suppliedfrom the transmit data conversion circuit 102, and supplies themodulating result to the spreading circuit 104. The spreading circuit104 performs code-spread processing by multiplying the signal modulatedby the modulation circuit 103 by a spreading code, and supplies thecode-spread transmit signal to the transmit circuit 105.

[0027] The transmit circuit 105 transmits the code-spread transmitsignal with the transmit power determined based on a specifying signalfor specifying the transmit power value supplied from the transmit powerdetermining circuit 113, to a mobile station via the transmit antenna106.

[0028] The receive circuit 108 converts a received signal received froma mobile station via the receive antenna 107 into a base band signal,and supplies the converted base band signal to the despreading circuit109.

[0029] The despreading circuit 109 recovers its pre-spread data byperforming despread process using correlation detection on the inputbase band signal, and supplies the recovered receive data to thedemodulation circuit 110. The demodulation circuit 110 demodulates thereceive data despread by the despreading circuit 109, and supplies thedemodulating result to the receive data conversion circuit 111.

[0030] The receive data conversion circuit 111 performs FEC decoding andCRC detection on the demodulated receive data, and outputs the decodingresult.

[0031] The synchronization determining circuit 112 determines thesynchronization state of the received signal based on the receive datademodulated by the demodulation circuit 110, and supplies the transmitpower determining circuit 113 with a synchronization determinationsignal indicating whether synchronization is established or out based onthe determining result. FIG. 2 is a block diagram showing theconfiguration of the synchronization determining circuit 112.

[0032] As shown in FIG. 2, the synchronization determining circuit 112inputs the demodulated signal supplied from the demodulation circuit 110into a known signal extraction circuit 112 a. The known signalextraction circuit 112 a extracts a known signal from the demodulatedsignal, and supplies the extracted signal to a pattern matching circuit112 b.

[0033] The pattern matching circuit 112 b performs pattern matching onthe known signal supplied from the known signal extraction circuit 112a. A determining circuit 112 c determines that synchronization isestablished, when the pattern matching result obtained by the patternmatching circuit 112 b indicates that the matching degree is at or abovea certain numeric value, and supplies the determining result to thetransmit power determining circuit 113.

[0034] Note that the synchronization determining circuit 112 may performthe determination using the CRC-error detection result supplied from thereceive data conversion circuit 111 and the determination based on thepattern matching result in combination. In this case, the determiningcircuit 112 c determines that synchronization of the received signal isestablished, when the conditions are met that an error rate, that is,the error detection result supplied from the receive data conversioncircuit 111, is within a predetermined range, and that the patternmatching result obtained by the pattern matching circuit 112 b indicatesthat the matching degree is at or above a certain numeric value.Thereby, the reliability of the synchronization determination result canbe raised further.

[0035] The transmit power determining circuit 113 determines thetransmit power based on the synchronization determination signalsupplied from the synchronization determining circuit 112, and suppliesa specifying signal specifying the determined transmit power value tothe transmit circuit 105.

[0036] Furthermore, a timing control circuit 114 controls the operationtimings and sequences of the entire communication apparatus 100.

[0037]FIG. 3 is a block diagram showing the configuration of thetransmit power determining circuit 113 of the communication apparatus100. As shown in FIG. 3, the transmit power determining circuit 113receives the demodulated signal supplied from the demodulation circuit110 by a transmit power control circuit 201. The transmit power controlcircuit 201 performs closed-loop transmit power control based on thedemodulated signal.

[0038] The closed-loop transmit power control is the mobile stationdetermines the transmit power of a signal to be sent in return to thebase station based on the transmit power control information from thebase station.

[0039] Here, the transmit power control circuit 201 determines thetransmit power value for each slot of the received signal (demodulatedsignal), and supplies the transmit power sequentially at the timings ofthe respective slots to each of a transmit power storage circuit 202 anda transmit power select circuit 203.

[0040] The transmit power control circuit 201 supplies the transmitpower values determined in this way to the transmit power storagecircuit 202 and also to the transmit power select circuit 203. Thetransmit power storage circuit 202 is configured to store transmit powervalues determined by the transmit power control circuit 201 for the pastN times, that is, N slots.

[0041] Specifically, when a new transmit power value is supplied fromthe transmit power control circuit 201, the transmit power storagecircuit 202 stores the new transmit power value instead of the earliesttransmit power value. Thus the transmit power storage circuit 202 alwaysstores transmit power values for the latest N times (N slots).

[0042] The transmit power values stored in the transmit power storagecircuit 202 are supplied to the transmit power select circuit 203 atpredetermined timings. Specifically, the transmit power select circuit203 selects one of a real-time transmit power value output from thetransmit power control circuit 201 or a past transmit power value storedin the transmit power storage circuit 202 based on the synchronizationdetermination signal supplied from the synchronization determiningcircuit 112.

[0043] In this case, when the synchronization determination signalsupplied from the synchronization determining circuit 112 indicates thatthe synchronization of the demodulated signal is established, thetransmit power select circuit 203 determines that the transmit powercontrol follows the received signal and selects a transmit power valueoutput from the transmit power control circuit 201, considering that thetransmit power value determined by the transmit power control circuit201 is reliable.

[0044] On the other hand, when the synchronization determination signalsupplied from the synchronization determining circuit 112 indicates thatthe synchronization of the demodulated signal is out, the transmit powerselect circuit 203 determines that the transmit power control does notfollow the received signal, and selects a transmit power value stored inthe transmit power storage circuit 202 instead of the transmit powervalue output from the transmit power control circuit 201 consideringthat the transmit power value determined by the transmit power controlcircuit 201 is hardly reliable.

[0045] Note that the synchronization determining circuit 112 determinesthe synchronization state for each frame of the received signal(demodulated signal). Therefore, when determining that thesynchronization is out, the synchronization determining circuit 112determines that the transmit power control does not follow the receivedsignal during all slots of the frame for which it determines.

[0046] Therefore, when receiving a determination result that thesynchronization is out via the synchronization determination signalsupplied from the synchronization determining circuit 112, the transmitpower select circuit 203 reads out a transmit power value earlier by oneframe, i.e. N slots composing the frame, from the transmit power storagecircuit 202.

[0047] Then the transmit power select circuit 203 determines a transmitpower value to be actually supplied to the transmit circuit 105 based onthe N'th past reliable transmit power value read out from the transmitpower storage circuit 202. Specifically, the transmit power selectcircuit 203 changes, over a predetermined number of slots' times, thetransmit power value being supplied to the transmit circuit 105, as atarget, the N'th past transmit power value read out from the transmitpower storage circuit 202. By thus gradually changing the transmit powervalue being supplied to the transmit circuit 105 over a predeterminedperiod rather than changing to the N'th past one at one time, theoperation of the transmit circuit 105 becomes stable.

[0048]FIG. 4 is a flow chart showing the procedure of setting thetransmit power by transmit power determining circuit 113. As shown inFIG. 4, the transmit power determining circuit 113, in step ST100, waitsfor the synchronization determination signal to be supplied from thesynchronization determining circuit 112. When the synchronizationdetermination signal is supplied, step ST101 is taken where the transmitpower determining circuit 113 determines whether or not thesynchronization is out from the synchronization determination resultdenoted by the then supplied synchronization determination signal.

[0049] When the result is negative, which means that the synchronizationis established, step ST103 is taken where the transmit power selectcircuit 203 of the transmit power determining circuit 113 selects thetransmit power value output from the transmit power control circuit 201mentioned above with reference to FIG. 3 to supply the transmit powervalue output from the transmit power control circuit 201, as it is, tothe transmit circuit 105. Thus, the closed-loop transmit power controlcontinues in the transmit power control circuit 201.

[0050] On the other hand, when the result is affirmative in step ST 101,which means that the synchronization is out, step ST102 is taken wherethe transmit power select circuit 203 of the transmit power determiningcircuit 113 selects a past transmit power stored in the transmit powerstorage circuit 202.

[0051] In this case, the transmit power select circuit 203 selects andreads out the transmit power value earlier by N slots (N=15) from amongthe past transmit power values stored in the transmit power storagecircuit 202. Specifically, in the CDMA communication scheme of thepresent embodiment, the transmit power value earlier by N slots (N=15)means the transmit power value corresponding to the last slot of thepast frame because one frame of the sent and received signals consistsof 15 slots.

[0052] Note that synchronization determination in the synchronizationdetermining circuit 112 is performed for each frame, so that, when theout-of-sync state is detected, the transmit power value corresponding tothe slot earlier by N slots (N=15) becomes the transmit power valuecorresponding to the last slot of the past frame where thesynchronization was established. Thus, the transmit power valuecorresponding to the most recent slot in the state where thesynchronization is established is read out by the out-of-sync state fromthe transmit power storage circuit 202.

[0053] Then the transmit power determining circuit 113, in step ST102,controls the transmit power value to gradually change from the transmitpower value immediately before the out-of-sync state is detected to theN slots past transmit power value read out from the transmit powerstorage circuit 202 over a predetermined period based on the N slotspast transmit power value read out from the transmit power storagecircuit 202. Note that the transmit power select circuit 203 stores thevalue of the transmit power just before supplied to the transmit circuit105 each time.

[0054]FIG. 5 is a schematic view for explaining the control of changingthe transmit power value to the N slots past transmit power value by thetransmit power select circuit 203. As shown in FIG. 5, in frames FR1,FR2, FR3, and the like, each consisting of 15 slots, the transmit powervalue is controlled to follow the level of the received signal by theclosed-loop transmit power control of the transmit power control circuit201 in the synchronization-established state as shown in, for example,the frame FR1.

[0055] On the other hand, when the out-of-sync state is detected in, forexample, the frame FR2, the out-of-sync state is recognized by thetransmit power determining circuit 113 receiving the synchronizationdetermination signal at time t13. Hence, at time t13 the transmit powerselect circuit 203 detects the out-of-sync state from thesynchronization determination signal, and selects the N slots pasttransmit power value from among the transmit power values for the past Nslots (N=15) stored at that time in the transmit power storage circuit202, output from the transmit power control circuit 201. This selectedthe N slots past transmit power value is the transmit power valuecorresponding to the last slot of the past frame FR1 where thesynchronization was established, just before the out-of-sync state isdetected in FIG. 5.

[0056] As described above, the transmit power value in the transmitpower storage circuit 202 which is to be selected when the transmitpower select circuit 203 detects the out-of-sync state is a transmitpower value at the most recent timing from among the past transmit powervalues determined under reliable conditions.

[0057] Then the transmit power select circuit 203 calculates thetransmit power value to be supplied to the transmit circuit 105 based onthe transmit power value selected and read out in this way from thetransmit power storage circuit 202 (step ST102). Specifically, as shownin FIG. 5, the transmit power value is changed from the transmit powervalue corresponding to the last slot of the frame FR2 where theout-of-sync state was detected to the N slots past transmit power value(the transmit power value of the last slot of the frame FR1) by stepsover a predetermined number of steps, i.e., over the one-frame period ofthe frame FR3 following the frame FR2 where the out-of-sync state wasdetected, based on the N slots past transmit power value (the lasttransmit power value of, e.g., the frame FR1 where the synchronizationwas established), while the changed and calculated transmit power valueis supplied to the transmit circuit 105 at the timing of each slot ofthe frame FR3, which is a timing for supplying the transmit power valueto the transmit circuit 105. Note that in the present embodiment, thetransmit power select circuit 203 changes the transmit power by stepsover the same number of steps as the number of slots of one frame (15slots).

[0058] In this manner, the transmit power value determined in the frameFR2 in the out-of-sync state is gradually returned to a reliabletransmit power value during the frame FR3 following the frame FR2. Asdescribed above, the transmit power control circuit 201 can perform theclosed-loop transmit power control following the transmit powercontrolled by the transmit power select circuit 203 because the transmitpower value does not rapidly change.

[0059] Note that if the synchronization is still out after theprocessing in step ST102, the transmit power select circuit 203maintains the transmit power value controlled in step ST102. Then, whenthe synchronization is restored, the transmit power value output fromthe transmit power control circuit 201 is selected.

[0060] As described above, according to the communication apparatus 100,when the synchronization of the received signal is established, thetransmit power control is performed using a transmit power valueobtained by the closed-loop transmit power control by the transmit powercontrol circuit 201, and when the synchronization of the received signalis out, the transmit power can be controlled avoiding rapid changesthereof by controlling the transmit power value to gradually return overa predetermined period to a transmit power value determined at a timingclosest to the current timing from among the past reliable transmitpower values determined when the synchronization was established, sothat the transmit power control in the transmit power control circuit201 can function smoothly even when the transmit power control in thetransmit power select circuit 203 deviates from the processing loop ofthe closed-loop transmit power control by the transmit power controlcircuit 201. Thus, the transmit and receive quality of the CDMA schemecan be secured.

[0061] While the above embodiment describes the case where the transmitpower select circuit 203 makes the transmit power value converge to atarget transmit power value by steps over the steps of one frame (15slots) when the synchronization is out, the present invention is notlimited to this. The point is to make the transmit power value graduallyconverge to a target value. For example, the transmit power value may bemade to converge to a target transmit power value by steps over thesteps of a half frame. The number of steps over which to make thetransmit power value converge to a target value can thus take variousnumbers.

[0062] Moreover, the above embodiment has described the case where thecircuit sections of the transmit power determining circuit 113 performsthe processing described above with reference to FIG. 4, but the presentinvention is not limited to this. A computer may be configured toexecute the processing procedure. In this case, it is required onlythat, having the processing procedure described above with reference toFIG. 4 stored as a program in a recording medium such as an opticaldisk, the computer be made to execute the program read out from therecording medium.

[0063] Furthermore, the above embodiment has described the case ofapplying the present invention to a mobile station apparatus, but thepresent invention is not limited to this. Applying the present inventionto a base station apparatus can also achieve the same above effect.

EMBODIMENT 2

[0064]FIG. 6 is a block diagram showing the configuration of acommunication apparatus 300 according to embodiment 2 of the presentinvention. The same parts as in FIG. 1 are denoted by the same referencenumerals with a detailed description thereof omitted.

[0065] The communication apparatus 300 shown in FIG. 6 differs from thecommunication apparatus 100 described above with reference to FIG. 1 inthe configuration of the transmit power determining circuit 313, and theothers are the same. FIG. 7 is a block diagram showing the configurationof the transmit power determining circuit 313. The same parts as in FIG.3 are denoted by the same reference numerals with a detailed descriptionthereof omitted. As shown in FIG. 7, the transmit power determiningcircuit 313 receives the demodulated signal supplied from thedemodulation circuit 110 by the transmit power control circuit 201. Thetransmit power control circuit 201 performs closed-loop transmit powercontrol based on the demodulated signal.

[0066] The transmit power control circuit 201 is configured to determinethe transmit power value for each slot of the received signal(demodulated signal), and supplies the determined transmit powersequentially at the timings of the respective slots to each of thetransmit power storage circuit 202 and the transmit power select circuit203.

[0067] The transmit power storage circuit 202 stores transmit powervalues supplied from the transmit power control circuit 201 for the pastN slots. The transmit power select circuit 203 selects one of areal-time transmit power value output from the transmit power controlcircuit 201 or a past transmit power value stored in the transmit powerstorage circuit 202 based on the synchronization determination signalsupplied from the synchronization determining circuit 112.

[0068] Upon detecting that the synchronization of the received signal isout via the synchronization determination signal, the transmit powerselect circuit 203 reads out the N-slots past transmit power valuestored in the transmit power storage circuit 202, and controls thetransmit power value being supplied to the transmit circuit 105 based onthe N-slots past transmit power value in the way described above withreference to FIG. 5.

[0069] In addition to this configuration, the transmit power determiningcircuit 313 further comprises a reliability detection circuit 301 and areliability determining circuit 302, and the reliability detectioncircuit 301 detects reliability of the demodulated signal based on thedemodulated signal supplied from the demodulation circuit 110.

[0070] Specifically, the reliability detection circuit 301 receives thedemodulated signal supplied from the demodulation circuit 110 by a powercomputing circuit 301 a. The power computing circuit 301 a computes apower value (I²+Q²) for the demodulated signal (I/Q signal) for eachsymbol, and supplies the computing result to a subsequent averagingcircuit 301 b.

[0071] The averaging circuit 301 b averages power values supplied fromthe power computing circuit 301 a over a plurality of slots, and obtainsthe reliability of the demodulated signal (received signal) based on theaveraging result. As this reliability, the receive level, aninterference level, SIR (Signal to Interference Ratio) and BER (BitError Rate) can be used. In the present embodiment, the case of usingthe receive level of the demodulated signal as the reliability will bedescribed.

[0072] The reliability detection circuit 301 supplies such reliabilityinformation (averaged level of the received signal over a plurality ofsymbols) to the reliability determining circuit 302. The reliabilitydetermining circuit 302 determines the reliability of the demodulatedsignal based on the reliability information supplied from thereliability detection circuit 301. The method of the determining is thatthe reliability determining circuit 302 determines whether or not thedemodulated signal is reliable depending on whether the reliabilityinformation is greater than a predetermined threshold value.

[0073] For example, when the receive level, which is the reliabilityinformation, is greater than the predetermined threshold value, it isdetermined that the reliability of the demodulated signal is high, andon the other hand, when the receive level is less than the predeterminedthreshold value, it is determined that the reliability of thedemodulated signal is low.

[0074] The reliability of the demodulated signal determined in this wayis supplied as a reliability determination signal from the reliabilitydetermining circuit 302 to the transmit power select circuit 203. Thetransmit power select circuit 203 selects one of a real-time transmitpower value output from the transmit power control circuit 201 or a pasttransmit power value stored in the transmit power storage circuit 202based on the synchronization determination signal supplied from thesynchronization determining circuit 112 and the reliabilitydetermination signal supplied from the reliability determining circuit302.

[0075] When selecting the transmit power value directly input from thetransmit power control circuit 201, the transmit power select circuit203 supplies the selected transmit power value, as it is, to thetransmit circuit 105, and when selecting a past transmit power valuestored in the transmit power storage circuit 202, the transmit powerselect circuit 203 computes a transmit power value based on the selectedtransmit power value by using the method described above with referenceto FIG. 5, and supplies the computed transmit power value to thetransmit circuit 105.

[0076]FIG. 8 is a flow chart showing the procedure of setting thetransmit power by transmit power determining circuit 313. As shown inFIG. 8, the transmit power determining circuit 313, in step ST200, waitsfor the synchronization determination signal to be supplied from thesynchronization determining circuit 112. When the synchronizationdetermination signal is supplied, step ST201 is taken where the transmitpower determining circuit 313 determines whether or not thesynchronization is out from the synchronization determination resultdenoted by the synchronization determination signal supplied.

[0077] When the result is negative, which means that the synchronizationis established, step ST203 is taken where the transmit power selectcircuit 203 of the transmit power determining circuit 313 selects thetransmit power value output from the transmit power control circuit 201mentioned with reference to FIG. 7 to supply the transmit power valueoutput from the transmit power control circuit 201, as it is, to thetransmit circuit 105. Thus, the closed-loop transmit power controlcontinues in the transmit power control circuit 201.

[0078] On the other hand, when the result in step ST201 is affirmative,which means that the synchronization is out, step ST202 is taken wherethe transmit power select circuit 203 of the transmit power determiningcircuit 313 determines whether or not the reliability is low based onthe reliability information output from the reliability determiningcircuit 302. When the result is negative, which means that thereliability is not reduced while the synchronization is out, step ST203is taken where the transmit power select circuit 203 of the transmitpower determining circuit 313 selects the transmit power value outputfrom the transmit power control circuit 201 to supply the transmit powervalue output from the transmit power control circuit 201, as it is, tothe transmit circuit 105.

[0079] On the other hand, when the result in step ST202 is affirmative,which means that the synchronization is out and the reliability of thedemodulated signal (received signal) is low, step ST204 is taken wherethe transmit power select circuit 203 of the transmit power determiningcircuit 313 selects a past transmit power value stored in the transmitpower storage circuit 202.

[0080] The process in step ST204 is the same as that in step ST102described above with reference to FIG. 4. The transmit power selectcircuit 203 selects and reads out the transmit power value earlier by Nslots (N=15) from among the past transmit power values stored in thetransmit power storage circuit 202, and according to the methoddescribed above with reference to FIG. 5, controls the transmit powervalue to gradually change over a predetermined period from the transmitpower value immediately before the out-of-sync state is detected to theN slots past transmit power value read out from the transmit powerstorage circuit 202.

[0081] In this manner, the transmit power determining circuit 313continues the closed-loop transmit power control as long as thereliability of the received signal (demodulated signal) is high, evenwhen the synchronization is out. Thus, provided that the closed-looptransmit power control is unlikely to be affected substantially if thereceived signal (demodulated signal) is reliable, in such cases, thefrequent occurrence of the control in deviation from the closed-looptransmit power control such as described above with reference to FIG. 5can be avoided by continuing the closed-loop transmit power control.Thus, the closed-loop transmit power control can be performed stably.

[0082] On the other hand, when the synchronization of the receivedsignal is out, the transmit power determining circuit 313 switches fromthe closed-loop transmit power control by the transmit power controlcircuit 201 to the transmit power value control based on a past transmitpower value by the transmit power select circuit 203 as long as thereliability of the received signal (demodulated signal) is low. Thus,when having fallen into a state where the closed-loop transmit powercontrol has difficulty in following, the transmit power controldescribed above with reference to FIG. 4 is immediately performed indeviation from the closed-loop transmit power control. As a result, thetransmit power determining circuit 313 does not follow instantaneousvariations of the received signal that it would follow if theclosed-loop transmit power control were being used.

[0083] In this manner, the transmit power determining circuit 313continues communication as far as possible, and immediately afterdetecting that the communication is out, switches from the closed-looptransmit power control to the transmit power control based on a pasttransmit power value. Thus, the transmit power value varies stablywithout following rapid changes of the received signal. Because thetransmit power value varies stably in this way, the possibility that thecurrent transmit power value has become transmit power value that theclosed-loop transmit power control can follow is high, when thecommunication connection is resumed after being in the communication-outstate. Hence, stable return to the closed-loop transmit power control ispossible in resuming the communication.

[0084] Note that when the synchronization is still out after the processin step ST204, the transmit power select circuit 203 is configured tomaintain the transmit power value controlled in step ST204, and afterthat, when the synchronization is restored, the transmit power valueoutput from the transmit power control circuit 201 is selected.

[0085] As described above, according to the communication apparatus 300,when the synchronization of the received signal is established, thetransmit power control is performed using a transmit power valueobtained by the closed-loop transmit power control by the transmit powercontrol circuit 201, and when the synchronization of the received signalis out, rapid changes of the transmit power value in controlling can beavoided by controlling the transmit power value to gradually return overa predetermined period to a transmit power value determined at a timingclosest to the current timing from among past reliable transmit powervalues determined when the synchronization was established, as long asthe reliability of the received signal is low. Thus, even after thetransmit power control based on a past transmit power value by thetransmit power select circuit 203 has been performed in deviation fromthe processing loop (of the closed-loop transmit power control) by thetransmit power control circuit 201, the transmit power control by thetransmit power control circuit 201 can be made to function smoothly.Therefore, the transmit and receive quality of the CDMA scheme can besecured.

[0086] While the above embodiment describes the case where the transmitpower select circuit 203 makes the transmit power value converge to atarget transmit power value by steps over the steps of one frame (15slots) when the synchronization is out, the present invention is notlimited to this. The point is to make the transmit power value graduallyconverge to a target value. For example, the transmit power value may bemade to converge to a target transmit power value by steps over thesteps of a half frame. The number of steps over which to make thetransmit power value converge to a target value can thus take variousnumbers.

[0087] Moreover, the above embodiment has described the case where thecircuit sections of the transmit power determining circuit 313 performthe processing described above with reference to FIG. 8, but the presentinvention is not limited to this. A computer may be configured toexecute the processing procedure. In this case, it is required onlythat, having the processing procedure described above with reference toFIG. 8 stored as a program in a recording medium such as an opticaldisk, the computer be made to execute the program read out from therecording medium.

[0088] Furthermore, the above embodiment has described the case ofapplying the present invention to a mobile station apparatus, but thepresent invention is not limited to this. Applying the present inventionto a base station apparatus can also achieve the same effect as above.

EMBODIMENT 3

[0089]FIG. 9 is a block diagram showing the configuration of acommunication apparatus 400 according to embodiment 3 of the presentinvention. The same parts as in FIG. 6 are denoted by the same referencenumerals with a detailed description thereof omitted.

[0090] The communication apparatus 400 shown in FIG. 9 differs from thecommunication apparatus 300 described above with reference to FIG. 6 inthe configuration of the transmit power determining circuit 413, and theothers are the same. FIG. 10 is a block diagram showing theconfiguration of the transmit power determining circuit 413. The sameparts as in FIG. 7 are denoted by the same reference numerals with adetailed description thereof omitted.

[0091] As shown in FIG. 10, the transmit power determining circuit 413supplies a reliability determination signal output from the reliabilitydetermining circuit 302 to a determination-result count circuit 401.

[0092] The determination-result count circuit 401, when the reliabilitydetermination signal supplied from the reliability determining circuit302 indicates the reliability being low, performs count. A minimum unitfor the count operation is a slot, but instead the average of per-slotreliability-determination results for a predetermined number of slotsmay be used. When the count value has reached a predetermined value, thedetermination result is notified to the transmit power select circuit203.

[0093] Note that each time the reliability signal supplied from thereliability determining circuit 302 indicates the reliability beinghigh, the determination-result count circuit 401 resets the count valueto zero. Thus, only when the reliability determination signal suppliedfrom the reliability determining circuit 302 indicates the reliabilityis high consecutively, the number of consecutive times of highreliability becomes greater than a predetermined number k, and only whenbeing greater than the predetermined number k, the determination-resultcount circuit 401 notifies the determination result to the transmitpower select circuit 203.

[0094] Therefore, only when the reliability is low consecutively, thetransmit power select circuit 203 performs the transmit power control(FIG. 5) using a past transmit power value stored in the transmit powerstorage circuit 202 instead of the transmit power value output from thetransmit power control circuit 201.

[0095]FIG. 11 is a flow chart showing the procedure of setting thetransmit power by the transmit power determining circuit 413. As shownin FIG. 11, the transmit power determining circuit 413, in step ST300,waits for the synchronization determination signal to be supplied fromthe synchronization determining circuit 112. When the synchronizationdetermination signal is supplied, step ST301 is taken where the transmitpower determining circuit 413 determines whether or not thesynchronization is out from the synchronization determination resultdenoted by the synchronization determination signal supplied.

[0096] When the result is negative, which means that the synchronizationis established, step ST303 is taken where the transmit power selectcircuit 203 of the transmit power determining circuit 413 selects thetransmit power value output from the transmit power control circuit 201mentioned with reference to FIG. 7 to supply the transmit power valueoutput from the transmit power control circuit 201, as it is, to thetransmit circuit 105. Thus, the closed-loop transmit power controlcontinues in the transmit power control circuit 201.

[0097] On the other hand, when the result in step ST301 is affirmative,which means that the synchronization is out, step ST302 is taken wherethe determination-result count circuit 413 determines whether or not thereliability of the demodulated signal (received signal) is low based onreliability information output from the reliability determining circuit302.

[0098] When the result is negative, which means that the transmit powerselect circuit 203 of the transmit power determining circuit 413 has notyet received the result of determining the count value from thedetermination-result count circuit 401, that is, the reliability is notreduced while the synchronization is out, the transmit power selectcircuit 203 selects the real-time transmit power value supplied from thetransmit power control circuit 201 to continue the closed-loop transmitpower control.

[0099] On the other hand, when the result in step ST302 is affirmative,which means that the reliability determining circuit 302 has suppliedthe reliability information indicating the reliability of thedemodulated signal being reduced to the determination-result countcircuit 401, the transmit power determining circuit 413 counts thenumber of times of having received the reliability informationindicating low reliability by the determination-result count circuit401, and increments the count value stored in a memory circuit (notshown in the drawing).

[0100] In this case, when the reliability information supplied from thereliability determining circuit 302 indicates the reliability beinghigh, the determination-result count circuit 401 resets the count valuestored in the memory circuit to zero. Thus, only when low reliability isdetected consecutively, the count value reaches the predetermined numberof times k.

[0101] Then the transmit power determining circuit 413, in step ST305,determines whether or not the counting result of thedetermination-result count circuit 401 is greater than the predeterminednumber of times k, that is, whether the reliability determining circuit302 has determined consecutively that the reliability of the demodulatedsignal is low, by the determination-result count circuit 401.

[0102] When the result is negative, which means that the reliability ofthe demodulated signal being low does not continue to reach thepredetermined number of times k, the transmit power select circuit 203of the transmit power determining circuit 413 selects the real-timetransmit power value supplied from the transmit power control circuit201 to continue the closed-loop transmit power control.

[0103] On the other hand, when the result in step ST305 is affirmative,which means that the reliability of the demodulated signal isconsecutively low, the determination-result count circuit 401 suppliesthe determination result to the transmit power select circuit 203, andstep ST306 is taken where the transmit power select circuit 203 of thetransmit power determining circuit 413 selects a past transmit powervalue stored in the transmit power storage circuit 202.

[0104] The process of step ST306 is the same as that of step ST102described above with reference to FIG. 4, the transmit power selectcircuit 203 selects and reads out the transmit power value earlier by Nslots (N=15) from among the past transmit power values stored in thetransmit power storage circuit 202, and the transmit power value iscontrolled to gradually change from the transmit power value immediatelybefore the out-of-sync state is detected to the N slots past transmitpower value read out from the transmit power storage circuit 202 over apredetermined period according to the method described above withreference to FIG. 5.

[0105] In this manner, even when the synchronization of the receivedsignal is out, the transmit power determining circuit 413 continues theclosed-loop transmit power control as long as the reliability of thereceived signal (demodulated signal) is high. Thus, provided that theclosed-loop transmit power control is unlikely to be affectedsubstantially if the received signal (demodulated signal) is reliable,in such cases, the closed-loop transmit power control is continued. Bythis means, the frequent occurrence of the control in deviation from theclosed-loop transmit power control such as described above withreference to FIG. 5 can be avoided. Thus, the closed-loop transmit powercontrol can be performed stably.

[0106] On the other hand, when the synchronization of the receivedsignal is out, the transmit power determining circuit 413 switches fromthe closed-loop transmit power control by the transmit power controlcircuit 201 to the transmit power value control based on a past transmitpower value by the transmit power select circuit 203 as long as thereliability of the received signal (demodulated signal) has beenconsecutively low. Thus, when having fallen into a state where theclosed-loop transmit power control has difficulty in following, thetransmit power control described above with reference to FIG. 5 isperformed in deviation from the closed-loop transmit power control. Inthis case, the transmit power determining circuit 413 switches to thetransmit power control based on a past transmit power value only whenthe reliability of the demodulated signal has been consecutively low,and thus the transmit power determining circuit 413 does not followinstantaneous variations of the received signal that it would follow ifthe closed-loop transmit power control were being used.

[0107] In this manner, the transmit power determining circuit 413continues communication as far as possible, and immediately afterdetecting that the communication is out, switches from the closed-looptransmit power control to the transmit power control based on a pasttransmit power value. Thus, the transmit power value varies stablywithout following rapid changes of the received signal. Because thetransmit power value varies stably in this way, the possibility that thecurrent transmit power value has become a value that the closed-looptransmit power control can follow is high when the communicationconnection is resumed after being in the communication-out state. Hence,stable return to the closed-loop transmit power control is possible inresuming the communication.

[0108] Note that when the synchronization is still out after the processin step ST306, the transmit power select circuit 203 is configured tomaintain the transmit power value controlled in step ST306, and afterthat, when the synchronization is restored, the transmit power valueoutput from the transmit power control circuit 201 is selected.

[0109] As described above, according to the communication apparatus 400,when the synchronization of the received signal is established, thetransmit power control is performed using a transmit power valueobtained by the closed-loop transmit power control by the transmit powercontrol circuit 201, and when the synchronization of the received signalis out, rapid changes of the transmit power value in controlling can beavoided by controlling the transmit power value to gradually return overa predetermined period to a transmit power value determined at a timingclosest to the current timing from among the past reliable transmitpower values determined when the synchronization was established, aslong as the reliability of the received signal (modulated signal) hasbeen consecutively low. Thus, even after the transmit power controlbased on a past transmit power value by the transmit power selectcircuit 203 has been performed in deviation from the processing loop (ofthe closed-loop transmit power control) by the transmit power controlcircuit 201, the transmit power control by the transmit power controlcircuit 201 can be made to function smoothly. Therefore, the transmitand receive quality of the CDMA scheme can be secured.

[0110] While the above embodiment describes the case where the transmitpower select circuit 203 makes the transmit power value converge to atarget transmit power value by steps over the steps of one frame (15slots) when the synchronization is out, the present invention is notlimited to this. The point is to make the transmit power value graduallyconverge to a target value. For example, the transmit power value may bemade to converge to a target transmit power value by steps over thesteps of a half frame. The number of steps over which to make thetransmit power value converge to a target value can thus take variousnumbers.

[0111] Moreover, the above embodiment has described the case where thecircuit sections of the transmit power determining circuit 413 performthe processing described above with reference to FIG. 11, but thepresent invention is not limited to this. A computer may be configuredto execute the processing procedure. In this case, it is required onlythat, having the processing procedure described above with reference toFIG. 11 stored as a program in a recording medium such as an opticaldisk, the computer be made to execute the program read out from therecording medium.

[0112] Furthermore, the above embodiment has described the case ofapplying the present invention to a mobile station apparatus, but thepresent invention is not limited to this. Applying the present inventionto a base station apparatus can also achieve the same effect as above.

[0113] The present description is based on Japanese Patent ApplicationNo.2002-114841 filed on Apr. 17, 2002, which is incorporated herein byreference.

INDUSTRIAL APPLICABILITY

[0114] The present invention can be applied to a communication apparatusused in a mobile communications system using the CDMA (Code DivisionMultiple Access) scheme and a transmit power control method for thecommunication apparatus.

What is claimed is:
 1. A communication apparatus comprising: a firsttransmit power control circuit that receives a transmit signaltransmitted from a mobile station or base station and controls atransmit power value of a signal to transmit to said mobile station orbase station based on the received signal; a transmit power valuestorage circuit that stores a predetermined number of past transmitpower values used in said first transmit power control circuit; asynchronization determining circuit that detects a synchronous state ofsaid received signal; and a second transmit power control circuit that,when the synchronous state is not maintained according to the detectionin said synchronization determining circuit, controls the transmit powervalue based on a past transmit power value corresponding to a time thesynchronous state was maintained, among the past transmit power valuesstored in said transmit power value storage circuit.
 2. Thecommunication apparatus according to claim 1, wherein, when thesynchronous state is not maintained, said second transmit power controlcircuit controls the transmit power value based on the past transmitpower value corresponding to a time said synchronous state wasmaintained, among the past transmit power values stored in said transmitpower value storage circuit, such that said transmit power value willconverge to said past transmit power value over a predetermined time. 3.The communication apparatus according to claim 1, further comprising areliability determining circuit that determines reliability of saidreceived signal, wherein, when said synchronous state is not maintainedand a determination result in said reliability determining circuitindicates a decrease in the reliability, said second transmit powercontrol circuit performs transmit power control based on said pasttransmit power value.
 4. The communication apparatus according to claim1, further comprising a reliability determining circuit that determinesreliability of said received signal, wherein, when the synchronous stateis not maintained and a determination result in said reliabilitydetermining circuit indicates a continuous decrease in the reliability,said second transmit power control circuit performs transmit powercontrol based on said past transmit power value.
 5. A transmit powercontrol method for a communication apparatus comprising: a firsttransmit power control step of receiving a transmit signal transmittedfrom a mobile station or base station and controlling a transmit powervalue of a signal to transmit to said mobile station or base stationbased on the received signal; a transmit power value storing step ofstoring a predetermined number of past transmit power values for use insaid transmit power control step; a synchronization determining step ofdetecting a synchronous state of said received signal; and a secondtransmit power control step of controlling a transmit power value basedon a past transmit power value corresponding to a time the synchronousstate was maintained, among the past transmit power values stored insaid transmit power value storing step, when said synchronous state isnot maintained according to a detection result in said synchronizationdetermining step.
 6. The transmit power control method for acommunication apparatus according to claim 5, wherein, when thesynchronous state is not maintained, said second transmit power controlstep controls the transmit power value based on a past transmit powervalue corresponding to a time said synchronous state was maintained,among the past transmit power values stored in said transmit powerstoring step, such that said transmit power value will converge to saidpast transmit power value over a predetermined time.
 7. The transmitpower control method for a communication apparatus according to claim 5,further comprising a reliability determining step of determiningreliability of said received signal, wherein, when the synchronous stateis not maintained and a determination result in said reliabilitydetermining step indicates a decrease in the reliability, said secondtransmit power control step performs transmit power control based onsaid past transmit power value.
 8. The transmit power control method fora communication apparatus according to claim 5, further comprising areliability determining step of determining reliability of said receivedsignal, wherein, when said synchronous state is not maintained and adetermination result in said reliability determining step indicates acontinuous decrease in the reliability, said second transmit powercontrol step performs transmit power control based on said past transmitpower value.